I’ve been using the free version of Unity but I never bothered to activate the trial. When I go into Help > Enter Serial Number it prompts me to activate and at the bottom of the window it says I can activate the 30-day trial of Unity Pro. However, when I do an online activation, there is no option to select the trial! It just says to activate the personal free version or the professional, then prompts for a serial number.
There is no trial anymore. Personal edition is the full featured engine. The only difference is splash screen, dark skin and access to some services ( which do have trials, i think) an limitation on not making over 100k from it or being a large business. No need for a trial anymore, just download personal and start building. 